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GCN Circular 10813

Subject
Swift UVOT and UVOT-enhanced XRT position for GRB 100528A
Date
2010-05-28T22:03:49Z (14 years ago)
From
Dirk Grupe at PSU/Swift-XRT <grupe@astro.psu.edu>
D. Grupe (PSU), M. Siegel (PSU), J. Gelbord (PSU),  P.A. Evans and
M.R. Goad (U. Leicester) report on behalf of the Swift team:

We report of the Swift UVOT and XRT detections of a bright source  
within the 5'
error radius of the SuperAGILE detected GRB 100528A (Del Monte et al.,
GCN Circ 10810) at a level of 2e-12 ergs/s/cm2 in the 0.3-10 keV band.
Swift started observing the field of GRB 100528A 42.5
ks after the AGILE detection and has observed it so far for 5 ks (two
orbits). At this point it is not obvious if the X-ray source is fading.
However, this X-ray source was not present during the ROSAT All-Sky
Survey. There is also an archival XMM data set that covers this
position (OBSID 0037990101, a 17ks exposure taken 2002-11-21).
There is no source detected at the position of the counter part.
Measuring the flux within a 30" radius of this position, the 4-sigma
upper limit of 5e-14 ergs/s/cm2 in the 0.2-12 keV band.  Most likely
the X-ray source found by the XRT is the X-ray afterglow of GRB 100528A.


Using 2497 s of XRT Photon Counting mode data and 2 UVOT
images, we find an astrometrically corrected X-ray position (using the
XRT-UVOT alignment and matching UVOT field sources to the USNO-B1
catalogue): RA, Dec =
311.14130, 27.80660 which is equivalent to:

RA (J2000):  20 44 33.92
Dec (J2000): +27 48 23.8

with an uncertainty of 2.1 arcsec (radius, 90% confidence).

This position may be improved as more data are received.  The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).

Using 4985 s of UVOT data take in the u, v and White filters,
we identify a faint uncataloged source within the XRT error circle
at a position in the white images of RA,DEC=311.14130, 27.80660 which
is equivalent to:

RA (J2000): 20 44 33.92
Dec (J2000): +27 48 23.8

with a 90%-confidence interval of about 0.60 arc sec. Preliminary
magnitudes using the  UVOT photometric system (Poole et al. 2008,
MNRAS, 383, 627) are:

FILTER     T_start(s)  T_stop    Exposure        Mag
=========================================================
white      43296       49881      1632     20.96+-0.13
v          44124       50777      1721     20.01+-0.35
u          42469       49036      1632     20.63+-0.24
=========================================================

The above magnitudes are not corrected for the Galactic extinction
corresponding to a reddening of E_{B-V} = 0.29 (Schlegel et al.,
1998, ApJS, 500, 525). The photometry is on the UVOT photometric
system described in Poole et al. (2008, MNRAS, 383, 627).



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